Technologies, such as touch sensitive screens, have allowed users to provide inputs to electronic devices, such as mobile phones and tablet computers, without requiring the use of a mouse and/or a keyboard. Examples of touch sensitive screens include capacitive sensors, pressure sensitive membranes, beam break techniques with circumferential light sources and sensors, and acoustic ranging techniques. However, these types of interfaces can only provide information to the device regarding the touch event, itself, and thus can be limited in application. In addition, such types of interfaces can be limited in the number of touch events that can be handled over a given amount of time, and can be prone to interpret unintended contacts, such as from a shirt cuff or palm, as touch events.
As an alternative to touch sensitive screens, optical motion and/or gesture recognition sensors have been developed, which can be used to recognize different motions of an object (e.g., a persons finger) within the sense region of the sensor. Typically, such optical sensors rely on multiple spatially dispersed light sources, multiple spatially dispersed light detectors, or both, to enable them to distinguish between motion in one or two directions. For example, one existing sensor includes a photodetector that is flanked on both sides by infrared light emitting diodes (IR-LEDs) spaced several tens of millimeters away from the photodetector to provide sufficient angular resolution, and a third IR-LED that is spaced several tens of millimeters away from the photodetector in a direction orthogonal to the line of the first two IR-LEDs and the photodetector. The IR-LEDs are pulsed one at a time, sequentially, such that the detected reflected light signals can be associated with the correct light source and its known location relative to the photodetector. From the detected reflected light pulses, a gesture recognition algorithm determines the direction and velocity of a target object, such as a user's finger.
A disadvantage of the exemplary configuration described above is that it requires at least three spatially dispersed light sources to detect movement in two directions (e.g., the x-direction and the y-direction), or at least two spatially dispersed light sources to detect movement in one direction (e.g., only the x-direction). Accordingly, such a configuration requires a relatively large footprint because of the spatial distances required between the light sources and the optical sensor.